(1) Field of the Invention
The present invention relates to a record material, more particularly to a pressure sensitive copy material.
(2) Description of the Prior Art
Heretofore, record materials, i.e., pressure sensitive copy papers have been known which are composed of a paper coated on the one side thereof with microcapsules containing a colorless electron donating agent (hereinafter referred to as the coupler) in a liquid state therein and another paper coated on the one side thereof with an electron accepting substance (hereinafter referred to as the developer) such as a clay or a polymeric material having an ability to develop a color by the reaction with the aforesaid coupler. When used, both the papers are superposed on each other so that the respective coated surfaces thereof may face each other, and pressure is then applied onto the superposed papers, so that a copy record is given thereby.
This type of record material has the following copy record mechanism: The microcapsules on the paper are ruptured by the pressure from a pen, a typewriter or the like in order to release a coupler solution therefrom, and the latter is then brought into contact with the developer with which the confronted paper has been coated, whereby a color is developed.
Further, another type of record material has been known in which the respective coating layers having such a color developing mechanism as described above are formed onto either surface of one paper, the microcapsule layer and the developer layer being disposed as an inside layer and an outside layer, respectively. In the case of this record material, the microcapsules, when used, are broken by a pressure from a pen, a typewriter or the like to consequently release a coupler solution therefrom, and the latter then contacts with the developer of the outside layer, thereby developing a color.
The coupler solution used in the aforesaid record material is a solution in which the electron donating coupler is dissolved in one or more hydrophobic solvents. The hydrophobic solvent used therein is required to satisfy the following requirements.
That is, these requirements are to be nontoxic; to have no uncomfortable odor; to be colorless or to have an extremely faint color; to be nonvolatile; to dissolve the coupler sufficiently; to be excellent in stability, after having dissolved the coupler; to be able to change into minute dispersions, when microcapsuled; to permit encapsulating the minute dispersions; to ensure a storage stability of the microcapsules; to permit coating a sheet material with the microcapsules uniformly with a suitable thickness; to allow a color developing reaction to occur, when the coupler contacts with the developer, and to accelerate a color development velocity; when a paper is coated a polymeric material which is the developer, to dissolve the polymeric material so as to enable a close contact with the coupler; to permit providing sharp color-developed images without blotting; and even after stored for a long period of time, to ensure the formation of the clear color-developed images.
Examples of the already known and industrially used solvents for the coupler in this kind of pressure sensitive copy material include diarylalkanes such as phenyl-xylyl-ethane, phenyl-isopropylphenylethane, phenyl-xylyl-methane; an alkylnaphthalene such as diisopropylnaphthalene; an alkylbiphenyl such as isopropylbiphenyl; and partially hydrogenated terphenyl.
In addition, as the solvents for the coupler, various diarylmethanes and diarylethanes have been suggested in U.S. Pat. No. 3,836,383, Japanese Patent Provisional Publication No. 15,613/1973 and U.K. Pat. No. 1,389,674. However, these suggested solvents do not satisfy the above mentioned requirements for the solvent, in particular, the requirements of the color development properties and the inhibition of an odor simultaneously.
Generally speaking, the solvent having a high color development velocity also has a low boiling point and strong odor. Inversely, a solvent having less odor has high boiling point and viscosity, and is poor in color development properties.